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Principle and design of time difference ultrasonic flowmeter

1 introduction

ultrasonic has many advantages in measuring the flow rate of gas and fluid. Compared with traditional mechanical flow meter and electromagnetic flow meter, it has high measurement accuracy, strong adaptability to pipe diameter, non-contact fluid, convenient use, easy digital management and so on. In recent years, due to the development of electronic technology, the cost of electronic components has decreased significantly, which has greatly reduced the manufacturing cost of ultrasonic flow meters with tensile load applied on the side of handle 1 or compressive load applied on the side of hammer 1. The ultrasonic flow should be appropriately reduced, and the weight meters of B thallium and C thallium have also begun to be popularized. Readers often ask questions about ultrasonic flow measurement. As popularization, we will write some special articles to introduce some relevant knowledge in order to promote and popularize the popularization and improvement of ultrasonic flow technology. This paper mainly introduces the principle and design of the most commonly used measurement method: time difference ultrasonic flowmeter

2 principle of time difference ultrasonic flowmeter

the working principle of transit time ultrasonic flowmeter is shown in Figure 1. It is an indirect measurement method that uses a pair of ultrasonic transducers to send and receive ultrasonic waves alternately (or at the same time) in opposite directions, indirectly measures the flow rate of the fluid by observing the time difference between the forward and reverse flow propagation of ultrasonic waves in the medium, and calculates the flow rate through the flow rate

Figure 1 Schematic diagram of ultrasonic flow measurement principle of time difference method

Figure 1 has two ultrasonic transducers: forward flow transducer and reverse flow transducer. The two transducers are installed on both sides of the fluid pipeline at a certain distance. The inner diameter of the pipeline is D, the path length of ultrasonic travel is l, the forward flow velocity of ultrasonic is Tu, the reverse flow velocity is TD, and the angle between the propagation direction of ultrasonic and the flow direction of fluid is θ。 Due to fluid flow, the time taken for ultrasonic wave to propagate along the length of L is shorter than that used for countercurrent propagation, and its time difference can be expressed by the following formula:

where: C is the sound velocity of ultrasonic wave in non flowing medium, V is the flow velocity of fluid medium, and the difference between Tu and TD is:

where x is the distance between two transducers in the direction of pipeline

for simplification, we assume that the velocity of fluid is a small amount compared with the velocity of ultrasonic wave in the medium. That is:

the above formula can be simplified as:

that is, the flow rate of the fluid is:

it can be seen that the flow rate of the fluid is directly proportional to the time difference between the forward and reverse flow propagation of ultrasonic wave

flow Q can be expressed as:

3 design of time difference ultrasonic flowmeter

Figure 2 is the principle block diagram of our designed ultrasonic flowmeter. There are mainly two ultrasonic transmitting units, a time measuring unit and a controller in the figure. They work together to complete the emission, acceptance and time difference measurement of ultrasound. Other peripheral units are mainly used for packaging and manufacturing functions such as parameter setting of measuring instruments, output, display and transmission of measuring data. Please refer to relevant materials, which will not be introduced here

Figure 2 electrical principle block diagram of ultrasonic flowmeter

4 conclusion

there are many ways to install the transducer of time difference ultrasonic flowmeter. Common types include external type, pipe section type, and interposing type. For example, interposing type can be generally used for household gas meters. No matter what kind of installation method, its principle is similar. For example, the intrusive formula is taken from the above formula θ= 0。

there are several other measurement methods based on different principles when ultrasonic waves are used for fluid measurement: Doppler frequency shift method, phase difference method, correlation method, etc., which have their own advantages and disadvantages, and can be selected according to different service conditions, measurement accuracy and other factors

with the rapid development of electronic technology, the popularization of ultrasonic technology, the reduction of product cost and the improvement of reliability, we believe that ultrasonic flow meters will become the most commonly used means in fluid measurement. (end)

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